1. Field of the Invention
The invention relates to non-destructive inspection of an annular sealing wiper extending at the surface of a bladed wheel drum of a turbine engine. More particularly, it relates to eddy current inspection of the edges of wipers that extend generally in groups of several wipers, each group being situated between the disks making up such a drum.
2. Description of the Related Art
In an airplane turbojet, a turbomachine such as a compressor has a bladed wheel drum mounted to rotate about its main axis. This drum, often referred to as a “spool”, carries all of the rotor blades. Each stage of the compressor has a ring of movable blades that are regularly spaced apart at the periphery of a disk. The assembled-together disks constitute the above-mentioned drum.
Between the rings of movable blades there are arranged rings of stator vanes. Sealing between two successive stages is obtained by co-operation between a ring of abradable material that is carried by the stationary vanes, and wipers that are secured to said drum. The wipers constitute kinds of rough annular ribs. Between two successive stages, sealing is generally provided by a plurality of parallel wipers (generally two to four of them).
In order to limit wiper wear over time, a strong material is deposited thereon, by means of a plasma method. This plasma deposit needs to be subjected to non-destructive inspection in order to identify any type of crack fault. The non-destructive inspection means most commonly used involve eddy current inspection. This type of inspection has until now been performed using a probe (high frequency coil) having an end that is moved along the edge of the wiper for inspection, while remaining directly in contact therewith.
Plasma deposition involves a certain amount of roughness on the wiper and this leads to the probe being worn rapidly.
Attempts have been made to remedy that problem by covering the wiper and the end of the probe in a film of polytetrafluoroethylene in order to protect the probe, to ensure good effectiveness of eddy current inspection, and to achieve low friction while the probe is moving relative to the wiper. That solution requires a very lengthy preparation time, in particular for depositing the film on each wiper. Those operations occupy several hours and there is also the cost of the film of polytetrafluoroethylene.